My 1990 740 SE, B200E engine, starts and runs ok untill warmed up. Then it cuts out, coughs and sometimes backfires. All the electrics still work and the dash lights don't light up, but the rev. counter drops back, not falling with engine revs. It will idle at about 200 revs., hunting and shaking a lot, but won't rev up. turning the ignition off and on again will restore things for a few seconds.
After a visit to a breakers I have tried various bits.
Temp. sensor, after testing with multi-meter and pan of water,anti-knock sensor,resistance ok; ignition switch, coil, fuel pressure control, ign. control unit, 3 different power stage amplifiers and a brand new fuel pump/ ignition relay. All without success.
Any ideas please?